Sound-reproducing means



April 1931. A. NAGELVOORT 1,802,826

SOUND REPRODUGING MEANS Filed July 3, 1929 2 Sheets-Sheet 1 April 8, 1931. A. NAGELVOORT SOUND REPRODUCING MEANS Filed July 3, 1 29 2 Sheets-Sheet 2 i' ////////////JW////////AivI gwuewto'o AiW//////////A ////////A'!VI Qch-i QQ N Nd gelxroor't' Patented Apr. 28, 1931 UNITED STATES PATENT OFFICE ADRIAAN NAG-ELVOOR'I', OF WILMINGTON, DELAWARE, ASSIGNOR TO DELAWARE CHEMICAL ENGINEERING COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE SOUND-REPRODUCING MEANS Application filed July 3, 1929. Serial 1%. "375,728.

This invention relates to sound reproducmg means; and it comprlses aslatted, relatively massive diaphragm with the several slats resonant to different frequencies, and" thing the same complicated way' as occurs with coupled electric circuits. The free vibrations are those depending upon the net ural note or fundamental of the diaphragm as a whole and they are, or may be, much more energetic and damp away more slowly than the forced vibrations. This is the main reason for making diaphragms thin and light; to lower the energy ratio of free vibrations to forced, vibrations. The use of paper and cloth diaphragms has the same purpose. In

all ordinary diaphragms, however, there is some mass and some resonance; and there is always a fundamental of the diaphragm as a Whole; this giving not only a distortion of the forced vibrations but ,also giving a background to theYvholeureproduction.

In sound reproduction, it is a well recognized fact that the response of the diaphragm to waves of various frequencies is not proportional to the amplitude of thewave. The diaphragm has its own periods of vibration and its response to impressed vibrations of frequencies near. its ownis ,exaggerated in degrees depending uponthe damping. A

resonating horn, where one is used, also great- 1y modifies waves passing through it. With any of the usual diaphragms, the resultant motion of the diaphragm and the disturbances impressed on air may be quite different from the vibrations impressed on it.

The electromagnetic reproducing units used to actuate diaphragms as a rule are quite eflicient; both in radio loud speakers and in phonographattachments. They deliver vibrations corresponding not only to the fundamental notes of an instrument but also to the overtones and harmonics on which the timbre of that instrument depends; giving them in their original ratios. So far as the reproducing unit is. concerned, with an ideal diaphragm, the simultaneous reproduction of a piccolo and of a violin would give each with its own quantitative relations between fundamental and harmonics; the two instruments would be readily discernible by theear. Actually, none of the diaphragms now in use does this. And for another thing, with the thin, light diaphragms in use there is a sensitiveness to shock excitation contributing to the noise background which radio listeners call static.

In the present invention, I depart from the usual practice and seek to increase free vibration and decrease forced vibration. With an equal application 'ofpower, more and truer response may be had with free vibration than with forced. To avoid production of a dominant fundamental, however, I subdivide my diaphragm into a multiplicity of what may be called sub-diaphragms, each of its own period or pitch, with ,the several periods or notes taken together covering an octave or more. Advantageous'ly, they cover the whole musical gamut. As free vibra-" tions tend to continue after the application of power my sub-diaphragms are damped by edgew-ise engagement with adjacent res onantareas. \I r In the present embodiment of my invention I make the diaphragm of parallel tuned slats, much like those of a marimba ,or. a Xylophone. Each slat has a fundamental note of its own, so that I really substitute a large number of minor fundamental \notes for one major fundamental note. These tuned ,slats are in edgewise' engagement, whereby they damp each other mutually; damping out the free vibrations when application of power ceases. Differential tuning of the slats may be accom lished by making them of diiferent materia s, of various hard and soft woods, for example,-or by using different thicknesses. Both expedients may be used together. Advantageously also, the slots taper from end to end. Where only one wood is used, this is advantageously walnut, as walnut in the present diaphragm gives a good response over the wholescale. Where be advan-' thereby, in effect, providing a multiplicity.

of parallel vertical rods of different tune.-

A diaphragm constructed as just described has a multiplicity of areas responsive to dirt -v ferent notes and there is always an area giving free vibrations with any musical tone. Forced oscillations also occur but these are of minor importance. i

In the accompanying illustrations I have shown, more or less diagrammatically, vari-,

ous embodiments of the described invention. Fig. 1 is a view in elevation ofi a slat type. of sound board with actuating mechanism and bridge shown in dotted line, the slats havin edgewise engagement;

Iig. 2 is an edge view of the dotted elements shown in Fig. 1; I

Fig. 3 shows theelements in Fig. 1 from an end, illustrating the differential thicknesses of the slats;

Fig. 4'is a sectional view on a larger scale showing another embodiment of my-inven-" tion Fig. 5 is a plan view of a form of my in-' vention having slats secured together at mem ers, and

meeting ges and the assemblage bridgd in unsymmetrical manner;

Fig. 6 is a side view of a bridge member;

Fi 7 is an end viewshowing twd bridge Fig. Sis a fragmentary I riew showing slats of diflerent material.

In the showing of Fig. 1, 15 slats are illustrated. By reference to Figs; 3 and 4, it will benoted that these slats are of difi'erent thicknesses and hence, of difierent musical pitch. It will also be noted that these slats are more or less tapered or wedge shape. As shown in Flg. 1, these slats are secured together by end braces ll) and are further yoked by a cross bridge 11 to which is attached the-pin of a diagrammaticallyshown actuating unit 12. It .will be noted that this bridge is 1% cated nearer one-end of than the other. I

In the structure of Figs. 5 slats are. cemented or glued together. As will be noted' from Fig. 8, aplurality of woods of difl'erent character is used; alternatthe slat assemblage l3, 7 and '8, the

ingv strips of balsa and of rosewood, for example. All of the strips, however, may be of the same wood and vary*merely in thickness. As a general rule, where all the strips are of the same kind of wood or the same kind of material, the thickest point occurring in' a slat is four times the thickness of the thinnest point occurring. The same relations may exist in using two woods of 'difierent density. If a wood is four times as dense as another wood, it is used in-a quarter of the thickness in securing the same pitch. In the structure of Fig'. 5, the strips are crossed by --unsymmetrically placed diagonal bridges 15 ;and 16 and a cross bridge 17 from side to side. This bridge subdivides the whole ,diaphragm into six unequal triangles. For the present purposes, the bridges may be regarded as composed of assembled parallel vertical rods of unequal height, vibrating'longitudinally andresponding to difi'erent tones.

What I claim is:-

1. In a sound reproducing diaphragm, a panel composed of a plurality (7f parallel abutting, mutually damping slats of difiering resonance. Y

2. In'a sound reproducing diaphragm, a panel composed of a plurality of parallel slats of differing resonance, said slats having edge-to-edge damping engagement.

3. In a sound reproducing diaphragm, a panel composed of a plurality of parallel engaging slats of differing resonance, said panel carrying a crossing bridge member engagingallsaid slats. 4. In the structure of claim 1, slats tapermg along their length. i

'5. In a sound reproducing diaphragm, a

edge damping engagement.

6. In asound reproducing diaphragm,'a panel. comprising a plurality of mutually damped slats of differing resonance, said slats being joined together along their edges, said joints preventin relative movement. of the slats at their joined edges.

7. In a sound reproducin diaphragm, a panel comprising mutually amped slats of differing resonance and node producing bridges placed unsymmetrically upon said pane i 8.- A sound reproducing diaphragm composed of a plurality of unsymmetrical subdiaphragms, said diaphragm comprising a plurality of slats having edge-to-edge dampmg engagement.

n testimony whereof, I have hereunto afixed my signature. I

ADRIAAN NAGELVOORT.

' panel comprising a plurality of slats of differing resonance, said slats having edge to 

